Every tube filling project reaches the same fork in the road: hot air sealing or ultrasonic sealing? Both weld the open end of a plastic or laminated tube shut — but they do it in completely different ways, at different costs, with different failure modes. Having specified both technologies across 100+ factory projects, here is the honest comparison, including the cases where I recommend the one we don’t build.
Hot air sealing is the better choice for most cosmetic tube applications: it produces strong hermetic seals on both PE plastic and ABL/PBL laminated tubes, costs significantly less to buy and maintain, and is the proven industry standard. Ultrasonic sealing wins in two specific cases — highly heat-sensitive formulas and lines that cannot guarantee a clean seal zone — at roughly 30–50% higher equipment cost.
Key Takeaways
- Hot air melts the tube’s inner PE layer with a precise jet of heated air before the jaws close; ultrasonic melts it with 20–35 kHz friction vibration under cold tooling.
- Both methods work only on weldable tubes (PE, ABL, PBL). Pure aluminum tubes are folded and crimped mechanically — neither technology applies.
- Ultrasonic’s real advantage is sealing through product contamination: the vibration displaces cream out of the seal zone. Hot air needs a clean zone — which a tail-cutting nozzle provides.
- Hot air’s advantages are cost, simplicity and material tolerance: one generator covers all tube sizes, while ultrasonic needs a tuned sonotrode per format.
- For sunscreen and cream production, hot air with a Swiss LEISTER generator remains the configuration we fit as standard.
About the author — Forester Xiang
Forester combines deep technical knowledge with 20+ years of global market experience. Having personally audited 100+ cosmetic and pharmaceutical factories across 30+ countries, he helps clients buy not just a machine, but a complete, compliant, and profitable packaging solution.
How Each Technology Works
Hot Air Sealing: Melt, Then Press
Hot air sealing works by blowing a precisely heated jet of air (typically 250–400°C) into the open end of the tube, melting the inner polyethylene layer, then closing cooled jaws to weld and crimp the seal in one motion. The jaws also emboss the batch number and any decorative pattern into the still-soft plastic. Seal quality depends on three settings — air temperature, blow time, and jaw pressure — which is why a stable generator matters: the TF-60 sunscreen cream tube filling and sealing machine uses a Swiss LEISTER unit precisely because its temperature holds within a narrow band shift after shift.
- Filled tube indexes to the heating station; nozzle blows hot air inside the tube end.
- Inner PE layer reaches melt temperature in under a second.
- Cold jaws close: weld, crimp pattern and batch code form simultaneously.
- Brief cooling under pressure locks the hermetic seal; trimmer cuts the end square.
Ultrasonic Sealing: Vibrate, Don’t Heat
Ultrasonic sealing presses the tube end between a vibrating sonotrode (20–35 kHz) and a fixed anvil; the high-frequency friction melts the inner layer from within while the tooling itself stays cold. Because the energy is generated inside the plastic, the vibration physically displaces any cream sitting in the seal zone — the one task hot air cannot do. The trade-offs: each tube diameter needs its own tuned sonotrode, the generator and converter cost considerably more, and seal aesthetics are limited to simpler patterns.
Hot Air vs Ultrasonic: Full Comparison Table
| Criterion | Hot Air Sealing | Ultrasonic Sealing |
|---|---|---|
| Working principle | Heated air melts inner layer; cold jaws weld & crimp | 20–35 kHz friction melts inner layer; cold tooling |
| Tube materials | PE, ABL, PBL — full range | PE, ABL, PBL (thick laminates need tuning) |
| Seal strength | Hermetic, full-width weld | Hermetic when tuned correctly |
| Product in seal zone | Needs clean zone (tail-cutting nozzle) | Vibration displaces residue — most tolerant |
| Heat exposure to product | Localized warming near tube end; needs small headspace | Minimal — best for heat-sensitive formulas |
| Seal aesthetics / coding | Crimp patterns + embossed batch code, single/double-sided print | Simpler patterns; coding usually separate |
| Changeover between tube sizes | Mold change only — same generator covers all sizes | Dedicated tuned sonotrode per diameter |
| Energy consumption | ~3 kW continuous generator | Lower — energy only during weld cycle |
| Equipment cost | Lower — industry baseline | Roughly 30–50% premium on the sealing station |
| Maintenance | Simple: heater element & air filter | Specialist: converter, booster, sonotrode wear |
| Typical users | Cosmetics, sunscreen, pharma ointments — the default | Heat-sensitive actives, food pastes, premium niches |
Score it by column and the pattern is clear: ultrasonic wins on contamination tolerance and heat exposure; hot air wins on everything related to cost, flexibility and day-to-day operation.
Which Should You Choose?
Choose hot air sealing if…
You run cosmetics, sunscreen, or ointments in PE or laminated tubes; you change tube sizes regularly; you want batch coding embossed in the seal; and you want the lowest cost of ownership. This covers the overwhelming majority of cosmetic tube lines, which is why hot air is the standard station on both the TF-60 and our general-purpose cosmetic tube filling sealing machine.
Choose ultrasonic sealing if…
Your formula contains genuinely heat-sensitive actives (certain enzymes, probiotics, some natural extracts), you must fill with zero headspace, or your product is so stringy that no nozzle keeps the seal zone perfectly clean. Then the 30–50% station premium and per-size sonotrodes are justified — and we will tell you so in the quotation stage.
A useful diagnostic from my factory visits: when a hot-air line produces leaking tubes, the cause is almost never the sealing technology — it is cream contaminating the seal zone from nozzle stringing, two stations upstream. Before paying the ultrasonic premium to “fix sealing”, fix the filling. The full diagnosis is in our guide to filling high-viscosity sunscreen cream.
One boundary case worth stating plainly: pure aluminum tubes use neither technology. Metal cannot be welded by hot air or ultrasonics — aluminum tubes are closed by mechanical folding and crimping on a dedicated station. If your brand runs both aluminum and plastic tubes, you need both closing methods, not a compromise.
Frequently Asked Questions
Which is better, hot air or ultrasonic tube sealing?
Hot air sealing is better for most cosmetic applications: lower equipment and maintenance cost, one generator covering all tube sizes, and embossed batch coding in the seal. Ultrasonic sealing is better only for heat-sensitive formulas or lines that cannot keep the seal zone clean, at roughly a 30–50% premium on the sealing station.
Can hot air sealing be used on laminated ABL/PBL tubes?
Yes. ABL and PBL laminated tubes have a polyethylene inner layer, which is exactly what hot air melts to form the weld. A stable generator such as the Swiss LEISTER unit on the TF-60 tube filling and sealing machine seals PE, ABL and PBL tubes hermetically with the same station — only the mold changes between formats.
Does either method work on aluminum tubes?
No. Pure aluminum cannot be welded by hot air or ultrasonic vibration. Aluminum tubes are closed mechanically — folded two or three times and crimped — on a dedicated folding station. Lines that run both aluminum and plastic tubes need both closing methods.
Why do hot-air sealed tubes leak?
The most common cause is product contamination in the seal zone from nozzle stringing during filling — not the sealing station itself. The remaining causes are settings: air temperature too low, blow time too short, or jaw pressure uneven. Fix the tail-cutting at the filling nozzle first, then verify the three seal settings against the tube supplier’s specification.
Which sealing method is cheaper to run?
Hot air is cheaper to buy and maintain; ultrasonic is cheaper in energy per tube because it only draws power during the weld cycle. Over a typical machine life, hot air’s lower purchase price, simpler maintenance and universal tooling outweigh the energy difference for almost all cosmetic lines — the exception is very high-volume operations running 24/7.
Not Sure Which Sealing Fits Your Formula?
Send me your formula type and tube specification. I’ll tell you straight whether standard hot air does the job — or whether your product is one of the genuine ultrasonic cases.
Ask Forester — Free Technical Answer
